It is narrated from Umm al-Mu'mineen Sayyidah Aisha (may Allah be pleased with her) that Sayyidah Fatimah bint Abi Hubaysh (may Allah be pleased with her) said to the Messenger of Allah (peace and blessings be upon him): "O Messenger of Allah! I do not remain pure, should I leave the prayer?" He (peace and blessings be upon him) said: "(What you consider to be menstruation) is blood from a vein, not menstruation. When menstruation comes, then leave the prayer, and when its days have passed according to estimation, wash the blood off and perform the prayer."
Hadith Referenceالسنن المأثورة / باب ما جاء في الصلاة على الراحلة / 135
Hadith Takhrijصحیح بخاری، الحيض، باب الاستحاضة، رقم: 306؛ صحیح مسلم، الحيض، باب المستحاضة وغسلها وصلاتها، رقم: 333